1. Field of the Invention
The present invention relates to an engine generator unit which includes an engine and an electric-power generator to be driven by the engine that are mounted within a space defined by a pipe-shaped framework.
2. Related Prior Art
Among general-purpose power supply devices suitable for outdoor use is the so-called open-type engine generator unit which includes an engine and an electric-power generator to be driven by the engine that are mounted within a space defined by a framework. Typical examples of such an open-type engine generator unit are shown in Japanese Patent Publication No. HEI 1-9452 and Japanese Utility Model Publication HEI 7-24922.
In the engine generator unit disclosed in Japanese Patent Publication No. HEI 1-9452, the engine and electric-power generator to be driven by the engine are mounted side by side within a space defined by a framework made of pipe members. Within the space, a muffler and an air cleaner are also provided alongside of the generator and engine, respectively, and a generally flat fuel tank is provided over the engine, generator, muffler and air cleaner so as to cover a substantially entire top region of the space above the engine and generator.
Similarly, in the engine generator unit disclosed in Japanese Utility Model Publication HEI 7-24922, the engine and electric-power generator to be driven by the engine are mounted side by side within a space defined by a protective framework made of pipe members. Within the space, a muffler enclosed by a muffler cover is disposed above the generator, and a generally flat fuel tank is provided over the engine, generator and muffler so as to cover a substantially entire top region of the space above the engine, generator and muffler.
With the engine generator unit disclosed in the No. HEI 1-9452 publication, however, the capacity (size) and position of the muffler, which becomes particularly hot during operation, have to be carefully chosen (and hence are subject to considerable limitations) because the engine, generator, muffler and air cleaner are packed together in the framework-defined limited space under the fuel tank. Also, the capacity of the fuel tank has to be carefully chosen (and hence is subject to considerable limitations) in order to prevent the fuel tank from interfering with the other components provided in the small space below the fuel tank; for example, there are needs to appropriately shape the underside of the fuel tank, to provide a buffering space for avoiding thermal influences from components lying underneath the fuel tank. The engine generator unit disclosed in the No. HEI-7-24922 publication faces similar inconveniences and problems.
It is accordingly an object of the present invention to provide an improved engine generator unit which can increase the capacity of the muffler while providing for a large capacity of the fuel tank.
To accomplish the above-mentioned object, the present invention provides an engine generator unit which comprises: a framework having vertical pipe frame portions at its four corners; an engine; an electric-power generator to be driven by the engine, the engine and the electric-power generator being provided coaxially in a direction of an engine output shaft within a space defined by the framework; a fuel tank disposed above the engine and electric-power generator between a pair of support members each spanning between a different pair of the vertical pipe frame portions; a muffler connected to an exhaust-discharging end of the engine and positioned adjacent the fuel tank in a side-by-side relation thereto; and a heat blocking cover covering top and side portions of the muffler, the heat blocking cover being placed between the pair of support members in such a way that a substantially entire top region of the space defined by the framework is covered with the fuel tank and the heat blocking cover.
With the arrangements that the muffler covered with the heat blocking cover is disposed above the engine and electric-power generator and adjacent the fuel tank in a side-by-side relation thereto and the fuel tank and heat blocking cover together cover a substantially entire top region of the space defined by the framework, the muffler in the inventive engine generator unit is less subject to limitations on its capacity (size) and mounting position than in the prior counterparts where the engine, generator, muffler etc. are packed in an extremely narrow space under the fuel tank. Thus, with the present invention, the size and hence capacity of the muffler can be increased with ease. Further, the present invention can effectively reduce undesired heat radiation from the muffler to the fuel tank by closing the top and side portions of the muffler with the heat blocking cover, so that adverse thermal influences of the muffler on the fuel tank can be reliably avoided even where the muffler is located close to the fuel tank. In addition, because the muffler is not placed under the fuel tank, the empty space under the fuel tank can be accessed or used with ease, and the bottom portion of the fuel tank can be increased in size, which thereby provides for an increased overall capacity of the fuel tank.
In a preferred implementation of the present invention, a cylinder of the engine is mounted in a downwardly tilted posture with respect to a general vertical axis of the engine generator unit, and the muffler is mounted with its general plane lying substantially horizontally above the cylinder of the engine in an orientation where a longitudinal axis of the muffler crosses the engine output shaft at right angles thereto. By thus tilting the engine cylinder, the overall height or profile of the engine can be significantly lowered, which leaves a relatively large empty space above the thus-lowered engine cylinder within the space surrounded by the framework. The relatively large empty space can be utilized to position the horizontal muffler substantially at right angles to the engine output shaft, with the result that a large-size muffler can be mounted within the space defined by the framework.
Preferably, the heat blocking cover is generally in the shape of an elongate semicylindrical bowl closed at opposite ends and opening downward to cover an upper surface of the muffler, and a cooling air passage is provided between the heat blocking cover and the muffler. The outer surface of the muffler can be cooled with cooling air flowing through the cooling air passage. Further, by the presence of the cooling air passage, the heat of the muffler is not transferred directly to the heat blocking cover so that the outer surface temperature of the heat blocking cover can be prevented from getting very high.
Further, in a preferred implementation of the present invention, the muffler has an exhaust port positioned near the distal end of the cylinder of the engine mounted in the downwardly tilted posture, and a control panel is disposed on a side of the engine generator unit opposite or remote from the exhaust port. With this arrangement, the exhaust from the muffler can be prevented from flowing toward the control panel, which is therefore not thermally influenced by the muffler exhaust and can be constantly maintained in a suitable operating condition for a human operator to appropriately manipulate the panel as necessary.
Preferably, the electric-power generator is an outer-rotor/multipolar-magnet generator that has an outer rotor functioning also as a flywheel of the engine, and it further comprises an electric power controller for converting an output from the outer-rotor/multipolar-magnet generator to electric power of a predetermined frequency. Here, an output from the outer-rotor/multipolar-magnet generator, rather than the conventional synchronous generator, is converted via the electric power controller into electric power of a predetermined frequency and the outer rotor can function also as the flywheel of the engine, which can eliminate a need for a separate flywheel. The dimension of the engine generator unit in the axial direction of the engine output shaft can be reduced accordingly. In addition, because the fuel tank and muffler are placed side by side above the engine and generator, the engine generator unit can be constructed compactly into a generally cubic configuration and therefore can be installed appropriately in a small mounting space.
Preferably, the framework includes a pair of upper horizontal pipe frame portions each connecting between a predetermined pair of the vertical pipe frame portions, and the pair of upper horizontal pipe frame portions provide grips that can be suitably used when the engine generator unit is to be carried by hand. Such upper horizontal pipe frame portions allow the engine generator unit of the present invention to be carried or handled with utmost facility.
With the arrangements that the engine and the electric-power generator are provided coaxially in the direction of the engine output shaft within the mounting space defined by the framework, the engine cylinder is mounted in the downwardly tilted posture and the muffler is disposed above the engine and generator and adjacent the fuel tank in a side-by-side relation thereto, the inventive engine generator unit can be reliably kept in good weight balance with its center of gravity set substantially set at the center of the space defined by the framework. As a result, the engine generator unit can be carried and handled with great facility, using the upper horizontal pipe frame portions as grips.